Coevolution of larval signalling and worker response can trigger developmental caste determination in social insects

Abstract

Eusocial insects belong to distinct queen and worker castes, which, in turn, can be divided into several morphologically specialised castes of workers. Caste determination typically occurs by differential nutrition of developing larvae. We present a model for the coevolution of larval signalling and worker task allocation – both modelled by flexible smooth reaction norms – to investigate the evolution of caste determination mechanisms and worker polymorphism. In our model, larvae evolve to signal their nutritional state to workers. The workers evolve to allocate time to foraging for resources versus feeding the brood, conditional on the larval signals and their body size. Worker polymorphism evolves under accelerating foraging returns of increasing body size, which causes selection to favour large foraging and small nursing workers. Worker castes emerge because larvae evolve to amplify their signals after obtaining some food, which causes them to receive more food, while the other larvae remain unfed. This leads to symmetry-breaking among the larvae who either are well-nourished or malnourished; thus, emerging as small or large workers. Our model demonstrates the evolution of nutrition-dependent caste determination and worker polymorphism by a self-reinforcement mechanism that evolves from the interplay of larval signalling and worker response to the signals.

Maternal manipulation of offspring size can trigger the evolution of eusociality in promiscuous species

“…This result matches the prediction of the diapause ground plan hypothesis that a nutrition-dependent developmental switch regulates the production of the worker- and queen-phenotype 20,25,26,50,51 . Accordingly, many eusocial insects with irreversible castes have a nutrition-dependent caste determination system where caste is determined by food obtained during larval development 52–54 .…”

Coevolution of larval signalling and worker response can trigger developmental caste determination in social insects

“…Simulation model code, data analysis scripts and simulation data are available under: [75]. Further results are provided in the electronic supplementary material [76].…”